Substituting for natural pulp-made paper, there has been proposed and practically used synthetic paper which comprises a base layer constituted by a biaxially stretched polypropylene film, and paper-like layers provided onto both surfaces of the base layer and constituted by a uniaxially stretched polypropylene film containing 8 to 65% by weight of inorganic fine powder. (Reference is made to Japanese Patent Publication No. 40794/71 and Japanese Patent Application (OPI) Nos. 141339/81 and 118437/81 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").)
The synthetic paper of this kind has fine pores around the particles of the inorganic fine powder as nuclei, and further, has a lot of elongated, cracks at its surfaces. Accordingly, the paper is light in weight, and excellent in dryness of printing ink, adhesion with printing ink, writing property with a pencil and water proofness.
To impart better offset printing property, this synthetic paper is used in the state where an aqueous solution of acryl-series copolymers, polyethyleneimines, or the like, is coated to the surfaces in an amount of 0.005 to 0.1 g/m.sup.2 as solid, and then dried. (Reference is made to Japanese Patent Application (OPI) Nos. 10624/75, 161478/75, 40883/73, and 149363/82.)
Since the paper-like layer is constituted by a stretched film of a thermoplastic resin containing inorganic fine powder, and since the coated resin layer is made thin in thickness so as not to exceed 0.1 micron, the surfaces of the synthetic paper are rough (Bekk index measured in accordance with JIS P-8119 is 100 to 2,000 seconds).
Before the coated resin layer has been applied, the paperlike layer of the synthetic paper is in such a state that the inorganic fine particles, which form the nuclei of fine pores and surface cracks as described above, partly project from the surfaces of thereof so that the inorganic fine particles are apt to come off from the surface layer (a so-called paper dust trouble). Undesirably, the paper dust trouble may cause deterioration in continuous printability due to the mixture of the coming-off particles into printing ink or may cause dust in computer rooms, CAD drawing rooms, and other so-called clean rooms.
In the case where a tack tape stuck onto a printed surface of the synthetic paper is stripped off, there is such a disadvantage that the printing ink is stripped off together because of weak surface strength of the paper.
The synthetic paper provided with a coated resin layer in order to improve offset printing properties as described in the latter case is a little superior in prevention of the paper dust trouble. The improvement, however, does not have much effect on the prevention of the paper dust trouble, since the applied layer is thin in thickness, for example, about 0.01 micron.
To prevent the paper dust trouble from occurring, there has been also proposed high-glossy synthetic paper in which a resin film layer containing no inorganic fine powder or a very little inorganic powder (of 3% by weight or less) is provided on the surface of the paper like layer (1b) containing the inorganic fine powder (Japanese Patent Application No. 124882/84 corresponding to Japanese Patent Application (OPI) No. 3748/86, and U.S. application Ser. No. 739,818). The paper is superior in that no dust, high surface strength and high gloss printing can be performed, but inferior in writing properties with a pencil and an aqueous ink pen. Furthermore, the paper has a defect that ink is not so rapidly dried.